1. Field
The following description relates to a charge pump circuit for generating a boosted voltage by boosting an input voltage, and a charge pump method thereof.
2. Description of Related Art
Diverse semiconductor devices operate internal circuits by using a voltage supplied from the exterior. As the kinds of the voltage used in the inside of the semiconductor device are very diverse, it is difficult to supply all the voltages to be used inside a semiconductor device from the exterior. Therefore, a semiconductor device is provided with an internal voltage generation circuit for generating voltage of a new level inside of the semiconductor device.
In particular, a device using a battery as a power source should generate a higher voltage than a power source voltage inputted from the exterior when the level of the power source voltage supplied from the battery is low and the driving voltages to be used in the inside of the semiconductor device are higher than the level of the power source voltage supplied from the battery. A DC-DC converter generates a higher voltage than an inputted voltage. There is a switching mode power supply (SMPS) type of DC-DC converter which uses an inductor. There is also a charge pump type of DC-DC converter which uses a capacitor. In an example of a mobile device, as the current consumption is not high, the charge pump type of DC-DC converter is usually used.
FIGS. 1A and 1B are schematic diagrams illustrating a charge pump circuit boosting an input voltage 1.5 times and outputting a boosted voltage. FIGS. 2A and 2B are schematic diagrams illustrating a charge pump circuit boosting an input voltage 2 times and outputting a boosted voltage.
Referring to FIGS. 1A and 1B, an example in which the input voltage is boosted 1.5 times will be described hereafter. FIG. 1A illustrates a phase 1 operation in which the input voltage is divided in such a manner that a first capacitor 101 and a second capacitor 102 are charged with a voltage of ½*VCIN, individually. FIG. 1B illustrates a phase 2 operation in which the input voltage VCIN is added to the voltage of ½*VCIN charged in the first and second capacitors 101 and 102 and a voltage of 1.5*VCIN is output as a boosted voltage AVDD.
An example in which an input voltage VCIN is boosted twice will be described with reference to FIGS. 2A and 2B. FIG. 2A shows an operation of phase 1 in which the first capacitor 101 is charged with the input voltage VCIN, the input voltage VCIN is added with the voltage of the second capacitor 102, and the sum is output as a boosted voltage AVDD (i.e., AVDD=2*VCIN). FIG. 2B shows an operation of phase 2 in which the second capacitor 102 is charged with the input voltage VCIN and the input voltage VCIN is added to the voltage VCIN of the first capacitor 101 and output as a boosted voltage AVDD (AVDD=2*VCIN). As the operations of FIGS. 2A and 2B are iterated, a voltage of input voltage*2 (i.e., doubled) is output as a boosted voltage AVDD.
Referring to FIGS. 1A and 1B with FIGS. 2A and 2B, while the first and second capacitors 101 and 102 are charged with the voltage of ½*VCIN in FIGS. 1A and 1B, the first and second capacitors 101 and 102 are charged with the voltage VCIN in FIGS. 2A and 2B. In other words, the level of voltage charged in the first and second capacitors 101 and 102 becomes different based on the boosting magnification, which is also referred to as the “boosting mode.” Therefore, most of the conventional charge pump circuits are designed not to change the boosting mode during an operation. Although the boosting mode is changed during the operation of a charge pump circuit, a great deal of noise is generated momentarily, which may lead to instable operation of the charge pump circuit.